1. Field of the Invention
The present invention relates to a method of magnetizing a multipolar magnetic annular body that is used as a magnetic encoder, used in detecting the rotation of various machines and equipments, or a rotor of a motor and also to a magnetizing apparatus used in the practice of such magnetization method.
2. Description of Related Art
This type of the magnetic encoder has been known, in which a plurality of neighboring tracks are each magnetized with magnetic N and S poles that alternate with each other in a direction circumferentially thereof. (See, for example, the Patent Documents 1 and 2 listed below.) The magnetic encoder disclosed in the Patent Document 1 is provided with a track for the detection of the rotational phase and another track for the detection of the position of origin. On the other hand, in the magnetic encoder disclosed in the Patent Document 2, a plurality of tracks having magnetic poles in which phases are displaced relative to each other are provided in neighboring relation to each other. The Patent Document 3 also listed below discloses positioning of two magnetic encoders, each having a single track, in neighboring relation to each other, in which the pitch between the magnetic poles in those tracks are differentiated from each other to enable the absolute angle to be detected. Also, the Patent Document 4 further listed below discloses a magnetizing technique in the manufacture of the magnetic encoder.    [Patent Document 1] JP Laid-open Patent Publication No. 2007-198847    [Patent Document 2] JP Published Int'l Application No. 2002-512687    [Patent Document 3] JP Laid-open Patent Publication No. 2008-233069    [Patent Document 4] JP Patent No. 4024472